1. Field of the Invention
The present invention relates to a photocatalyst composite comprising a substrate having photocatalyst particles adhered thereon and a process for producing the same.
2. Description of Related Art
Exposure of photocatalyst particles to an irradiation of a wavelength corresponding to not less than the band gap energy causes the photoexcitation of electrons into a conduction band with a corresponding generation of holes in a valence band. The strong reduction power of the electrons and the strong oxidation power of the holes generated by this optical excitation have been utilized in decomposition and purification of organic materials as well as in decomposition of water. The photocatalyst particles to be used in such treatments are usually deposited on a substrate of dimensions larger than the photocatalyst particles in order to prevent them from scattering into the air or exhausting out of the system and subsequently to provide for easy separation of the photocatalyst from the treatment system. The deposition of photocatalyst particles on a substrate has been accomplished by a method comprising sintering the photocatalyst particles on the substrate at a temperature of 400.degree. C. or higher to adhere the particles to the substrate, or a method comprising spraying a precursor, which can be converted to photocatalyst through thermal decomposition, onto a substrate heated at a temperature of about 400.degree. C., thereby adhering the particles on the substrate. Alternatively, there has been proposed a method immobilizing photocatalyst particles using a certain type of fluorinated polymer. For example, Japanese Patent KOKAI (Laid-open) No. Hei 4-284851 discloses a method comprising laminating a mixture of photocatalyst particles and a fluorinated polymer and compressing the laminate under a pressure. Japanese Patent KOKAI (Laid-open) No. Hei 4-334552 discloses a method comprising thermally fusing a fluorinated polymer to adhere photocatalyst particles thereto.
Recently, an attempt has been made to use photocatalyst particles for decomposition of deleterious materials, malodorous materials and oily substances in the waste products produced daily in inhabitant circumstances as well as purification and sterilization of the waste products. Thus the photocatalyst particles have found ever broadening areas of application. In this regard, there is a need for a method capable of adhering firmly photocatalyst particles onto any substrate, which adhesion can be maintained over an extended period of time, without losing their photocatalytic function. Unfortunately, the prior art methods as described above suffer from insufficient adhesion strength as being susceptible to delamination under external pressure, and they require heating at high temperatures so that they can not apply to a substrate not resistant to heat such as plastics, interior materials such as office walls and the surfaces of various products which are difficult to heat, and the like. In addition, there are problems that the thermal treatments at high temperatures cause the photocatalyst particles to reduce their specific surface area resulting in a reduction in their photocatalytic function. Moreover, there may be required specific means such as devices for adhering under pressure, or fusing under heat.